The present invention relates to an igniting apparatus for internal combustion engines, which carrys out the ignition of air-fuel mixture with an electric arc discharge.
In an igniting apparatus igniting the mixture with the electric arc discharge according to the prior art, an ignition plug having an earthed electrode and a central electrode has been used, which ignition plug is mounted in the engine with both the electrodes being exposed into the combustion chamber to ignite and burn air-fuel mixture. In this arrangement, when the load on the engine is small i.e. the vacuum pressure in an intake manifold is high or the air-fuel ratio of mixture is large i.e. the mixture is lean, the ignitability is reduced.
In the usual internal combustion engine, in order to reduce the amounts of unburned hydrocarbon, carbon monoxide and nitrogen oxide included in exhaust gas, it is preferable to burn the mixture of the large air-fuel ratio i.e. the lean mixture. However, according to the prior ignition arrangement as described hereinbefore, the ignition for the mixture gas having a large air-fuel ratio is almost impossible.
An internal combustion engine comprising a main combustion chamber and an auxiliary combustion chamber provided with an ignition plug has been known. In this engine of the prior art, ignitable mixture i.e. mixture having an air-fuel ratio easily combustible is supplied to the auxiliary combustion chamber and ignited by the ignition plug, and then the ignition gas jets into the main combustion chamber from the auxiliary combustion chamber. The lean mixture in the main combustion chamber is burned by the ignited gas jetted thereto.
In the ignition system as described above, in order to produce within the auxiliary combustion chamber mixture different in an air-fuel ratio from mixture supplied to the main combustion chamber, it is necessary to separately provide an intake valve or a fuel injection valve in the auxiliary combustion chamber, so that the constructions of the fuel supply system of an engine may be complicated. Further, in this prior engine, there is such disadvantage that it is impossible to make the capacity of the auxiliary combustion chamber smaller than a certain value.
In usual internal combustion engine, the cause making wrong the ignitability of the lean mixture is as follows.
The arc discharge for the ignition generates concentratively at the spark gap defined by the central electrode and the earthed electrode in a combustion chamber and there is no turburent flow of the mixture at the position adjacent the spark gap of the ignition plug, so that even if the energy of the arc discharge is made high, part of the mixture to be activated by the arc discharge is a limited part existing nearly to the spark gap. These phenomena result that the probability of conduction of the energy for fuel particles is low and even if nuclei of flame generate the sizes of the nuclei do not reach a certain value and therefore, the desired energy for activating the fuel particles of mixture surrounding the nucleus of flame and extending the surface of the flame locks. As the energy of the nucleus of flame is unsufficient as above, the energy is absorbed by the fuel particles yet not burned existing nearly thereto and become extinct.
In general, an electromagnetic coil so called an ignition coil is used in order to generate the arc discharge. Such part of the air-fuel mixture as being under the influence of the arc discharge in the cylinders of engine is not ignited only but also activated by the arc discharge. This activation serves the acceleration of combustion of the mixture. Therefore, the energy of an electric arc discharge is influenced by the capacity of the ignition coil. An ignition coil being able to supply high energy is advantageous in relation to the ignition of mixture. An ignition coil according to the prior art only supply an electric energy of about 10-200 mJ and as the intencity of the electric current of arc discharge is restricted by the high impedance of the secondary coil of the ignition coil, the energy discharge level of arc discharge within a unit time is very low. It is impossible, within a certain limited period, to supply a sufficient energy to the mixture.
A main object of the present invention is to dissolve disadvantages due to the prior igniting apparatus as aforesaid and to provide a novel igniting apparatus being able to easily ignite lean mixture having a large air-fuel ratio.
An object of the present invention is to provide an igniting apparatus having an ignition electric source, of which the electric current of discharge is larger than that of the prior igniting apparatus, thereby a large energy can be supplied to the air-fuel mixture gas.
According to the present invention, an spark gap is provided at a communicating opening communicating the auxiliary combustion chamber to the main combustion chamber of the cylinder of engine and combustion gap passing through the communicating opening is energized extensively at high degree, so that the ignitability of an igniting apparatus can be improved.
Further, according to the present invention, the ignition effectiveness of an igniting apparatus can be sufficiently obtained, even if the capacity of an auxiliary combustion chamber is small in comparison with the usual engines. This matter possibly results that the auxiliary combustion chamber can be provided within an ignition plug without particularly providing an auxiliary combustion chamber in a cylinder head of an engine. If the ignition plug, as described above, having an auxiliary combustion chamber is used in the usual engine, the igniting apparatus according to the present invention could be applied to the usual engine.
In the igniting apparatus of the present invention, as aforesaid, mixture in an engine cylinder is effectively burnt by injecting combustion gas generated in an auxiliary combustion chamber into a main combustion chamber. Further, a spark gap is provided in the communicating opening or near thereto, so that the gas passing through said opening is activated (ionized) by the electro arc discharge. This activation increase the combustion efficiency and the velocity of the injecting gas into the main combustion chamber. In general, combustion gas i.e. burnt gas to be exhausted has a tendency of remaining within an auxiliary combustion chamber, so that the ignition for fresh mixture supplied into the auxiliary combustion chamber may be difficult. However, according to the present invention, as the spark gap is formed in the communicating opening or near thereto, even if the burnt gas (burnt material to be exhausted) remains in the innermost part of the auxiliary combustion chamber after completion of an exhaust stroke, new mixture gas to be ignited easily enters into the auxiliary combustion chamber through the communicating opening in a compression stroke and the new mixture gas is subjected to the electric arc discharge in the spark gap. Therefore, the ignition for the mixture gas is very easy.
In usual internal combustion engines, when the engine is under the condition of an idling operation, starting operation or low loading operation, particularly when the engine is under such condition that the temperature of the engine is low, the combustion temperature of a lean mixture gas intaked into the cylinder is low and the propagation of flame of the combustion is poor. In the present invention, the electric discharge for igniting the mixture is carried out in or at the position near the communicating opening formed between the auxiliary combustion chamber and the main combustion chamber, so that the mixture gas passing through the communicating opening is able to obtain high energy from the electric discharge arc. In the gas supplied the high energy, the jet velocity of the combustion gas (burnt gas) jetting into the main combustion chamber through the communicating opening is high, so that a highly effective propagation of flame can be obtained. This results that even when the temperature of engine is low and the intaked mixture is lean, good combustion effects can be obtained.
In the igniting apparatus according to the present invention, the spark gap is provided within or adjacent to the communicating opening formed between the main and auxiliary combustion chambers. A lean mixture gas is sucked into the main combustion chamber. In a certain case, lean and uniform mixture is supplied in the main and auxiliary combustion chambers respectively.
In the actual embodiments of the present invention, the electric arc discharge is carried out successively from a certain time in a compression stroke or when the mixture is introduced into the auxiliary combustion chamber, the electric arc discharge is once carried out, and then, when the combustion gas generated by burning said introduced mixture in the auxiliary combustion chamber jets into the main combustion chamber, a further electric arc discharge is once generated.
As described above, according to the present invention, as even a lean mixture gas can be easily burnt, an engine can be operated by the lean mixture. If the lean mixture is used for an engine, nitrogen oxide, hydrocarbon and carbon monoxide included in an exhaust gas (combustion gas) are decreased in comparison with the case of use of a rich mixture gas. Further, according to the igniting apparatus of the present invention, even if a vacuum pressure in an intake manifold is high, an effective ignition can be obtained. This results that the engine stall phenomena under low loading condition is prevented.
An igniting electric source apparatus of the igniting apparatus aforementioned, according to the present invention, comprises a high voltage electric source device and a low voltage electric source device. The high voltage electric source device causes an ignition plug to carry out an initial arc discharge. The low voltage electric source device discharges an electric charge stored in a capacitor by being induced by the initial arc discharge due to the high voltage electric source device. The electric charge stored in the capacitor is given to the ignition plug (spark plug) by the discharge of the capacitor. This discharge current due to the low voltage electric source device is relatively large. The electric arc discharge also in the ignition plug can be maintained for a long time in comparison with that in a prior igniting electric apparatus for the electric arc discharge. In the prior igniting electric apparatus, only an instantaneous high voltage discharge (corresponding to the initial arc discharge in the present invention) is generated in the ignition plug.
In the present invention, a high voltage electric power from the high voltage electric source device and a low voltage electric power (This voltage is of low in comparison with the high voltage supplied from the high voltage electric source device.) from the low voltage electric source device are supplied to the spark gap successively. A contact breaker and an electromagnetic induction coil, as well known, are employed for the high voltage electric source device, while the circuit having particular constructions of the present invention is used for the low voltage electric source device. These electric source devices are connected to the spark gap in parallel. In a practical circuit construction, rectifiers are provided in the respective circuits for preventing current leakage between these circuits.
The electric power supplied from the low voltage electric source device should be supplied to the electric discharge electrode of spark gap immediately after the initial electric discharge was developed in the spark gap by the high voltage electric source device to form an electric discharge path. For this purpose a capacitor and a resistor deciding the time constant of the condenser are connected to the electric source in the low voltage electric source device. Therefore, the electric power from the low electric source device is stored temporarily into the capacitor and this stored electric energy is discharged immediately after the initial electric discharge, so that the continuous discharge generates between the electric discharge electrodes of spark gap.
In the present invention, as aforesaid, the continuous discharge of low voltage is carried out at the spark gap following the electric discharge of high voltage. This effect is very useful for igniting the air-fuel mixture in a internal combustion engine, because in the ignition of the air-fuel mixture, the more the energy given from the electric arc discharge to the air-fuel mixture is larger, the more advantages are obtained. When the energy given to the mixture is large, the mixture is activated by the said energy over large extent.
The igniting electric source apparatus, as aforesaid, is very effective for the internal combustion engine having the spark gap within or adjacent to the communicating opening formed between the main combustion chamber and the auxiliary combustion chamber. In such internal combustion engine, the mixture gas supplied to the auxiliary combustion chamber is ignited by the electric arc discharge generated at the spark gap and then the combustion gas produced by the said ignition jets into the main combustion chamber and ignites mixture gas already supplied to the main combustion chamber. In this case, if the electric arc discharge is continuously carried out for a time, it is possible not only to ignites the mixture but to give effectively the combustion gas large energy. Supplying of the large energy to the combustion gas develops good combustion of the mixture in the main combustion chamber.
Other and further objects, features and advantages of the present invention will appear from the following description referring to the accompanying Drawings.